Outline

Objective: InfinOH is a communicating hydrocephalus with infratentorial intracisternal CSF-pathway obstruction, which can be treated successfully by endoscopic third ventriculostomy (ETV). The reported success-rate is around 70%. Various cases are found among patients with idiopathic normal pressure hydrocephalus (iNPH), but the frequency is unknown. Undetected InfinOHs in NPH patients means unnecessary shunt surgeries were ETV would be an alternative with similar results but less complications and less costs. A MRI-analysis of all iNPH-patients is necessary to find out the prevalence of InfinOHs and to assess the importance of differentiating "normal" iNPH and InfinOH.

Methods: Between August 2005 and June 2009 165 idiopathic NPH patients were treated. In all cases additional high resolution mid sagittal T2 weighted MRI scans were performed and analyzed for InfinOH: Diagnosis was confirmed, when the aqueduct and the fourth ventricle outflows were patent and the floor of the 3rd ventricle bulged downward simultaneously as well as the lamina terminalis pushed forward.

Results: From the 165 NPH patients treated surgically, 21 patients with clinical signs of iNPH showed the MRI-criteria of InfInOH corresponding 12,7%. The mean age of InfinOH patients were 56,7 years (range: 35–76 years) versus 72,2 years (range: 25–87 years) in the remaining iNPH patients. All InfinOH-patients were treated with ETV, all other pat. were treated with vp-shunts.

Conclusions: InfinOH is not frequently found in iNPH patients (12,7%). However, to neglect this subgroup means almost 13% of patients would be treated with a suboptimal vp-shunt instead of ETV accepting more complications all over. Focusing our attention to InfinOH could help to improve patients' selection for ETV or shunt, could reduce complications and costs.